Patent Literature 1 discloses a speed feedback loop that estimates an equivalent rigid body speed that is an output speed of a motor in the case of driving only an equivalent rigid body system, except a mechanical resonance system, of a load machine, based on a torque command, obtains a differential speed between the equivalent rigid body speed and the motor speed, and returns a differential speed between the differential speed and the motor speed in order to suppress an influence of the mechanical resonance system.